Multicolor, multilayer photographic elements are well known in the art. Such materials generally have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. Each layer has components useful for forming a particular color in an image. Typically, they utilize color forming couplers that form yellow, magenta and cyan dyes in the sensitized layers during processing.
After color development, it is necessary to remove the silver image that is formed coincident with the dye image. This can be done by oxidizing the silver using a suitable oxidizing agent, commonly referred to as a bleaching agent, followed by dissolving the silver halide so formed using what is known as a fixing agent.
A commercially important process intended for use with color reversal photographic elements that contain color couplers in the emulsion layers, or layers contiguous thereto, uses the following sequence of processing steps: first developing, washing, reversal bath, color developing, bleaching, fixing, washing and stabilizing.
In the past, in continuous processing methods, including processing of reversal color materials, the various processing solutions have been discarded after use. However, more recently, used processing solutions have been collected and reused, at least in part because of the environmental problems the waste solutions create, as well as the high costs in collection and discard of the solutions. Thus, used solutions have been reused by adding them to the processing baths as "replenishers" to the various solutions. Considerable efforts are being carried out in the industry to find ways to regenerate the components of the waste solutions so they can be reused as replenishers, further reducing waste streams. For example, a bleach replenishing composition is added to the bleach tank to keep the necessary components at the appropriate levels. This bleach replenisher can be composed of, in part, bleach composition overflow.
As environmental needs increase in various countries, the industry is striving to find ways to further reduce photoprocessing effluent from the various processing baths. Thus, efforts have been made to regenerate the bleaching solution overflow and to supply the regenerated replenisher solution to the bleach tank as the replenishment solution. One known bleach regenerator solution for reversal color processes is sold by Tetenal of Germany (sold as Tetenal Bleachbath E6/E6AR BL-RCY), which has a pH of about 7, and contains a relatively high bromide ion concentration (approximately 190-210 g/l).
There is also a desire in the industry to use a more concentrated bleach regenerator so more bleaching solution overflow can be utilized to make the bleach replenisher, thereby reducing effluent even further. The commercial product available from Tetenal, however, has limited shelf life stability at its "neutral" pH. It was considered that its pH might be lowered to increase stability, but when this was done, its solubility was decreased and precipitation resulted after several days. Another problem with the commercial Tetenal regenerator solution is that when acid is added to it to lower its pH to the level needed for converting it to a regenerated replenisher, the bleaching capacity of the resultant bleach tank solution is degraded.
There is a need therefore for a more stable bleach regenerator composition that can be used in highly concentrated form to provide a regenerated bleach replenisher at lower pH.